TEHRAN, YJC. -- Longtime U.S. diplomat Ryan Crocker says that when dealing with Iran, negotiations and concessions would be far more effective than tougher sanctions.

Ryan Crocker has long been viewed as America's indispensable diplomat in the Muslim world. President George W. Bush named him ambassador to Iraq in 2007 to rescue a failing policy, and four years later, President Obama dispatched him to salvage the U.S. mission in Afghanistan.

But Crocker, who Bush once lauded as "America's Lawrence of Arabia," now says his former bosses are fumbling the most worrisome Mideast threat America faces: Iran's nuclear program.

"Sanctions are easy to do, and afterwards we can tell ourselves that, 'By God, we've really stuck it to them,'" Crocker said in an interview. "But it seems to me that the more you press this regime, the more they dig in."

Crocker is among 35 high-powered foreign policy and intelligence veterans, some with extensive Middle East experience, who are pushing the White House and Congress to change course to persuade Iran to curb its nuclear ambitions.

The bipartisan group, which calls itself the Iran Project, includes former Sen. Richard G. Lugar (R-Ind.), former CIA Director Michael Hayden, former U.S. ambassador to Russia Thomas Pickering and veteran diplomat James Dobbins, who recently rejoined government as Obama's special representative for Afghanistan and Pakistan.

Crocker and the group aren't urging that sanctions be immediately dropped. By choking off trade in key technologies, he said, they have slowed Iran's nuclear program and its military modernization. At the same time, they argue, a hard line in and of itself won't work.

They would seem to face long odds. Successive U.S. administrations have hit Iran with economic penalties since the Islamic Revolution in 1979. Recent U.S. and European sanctions have cut Iran's lucrative oil exports in half, undermined the value of its currency and choked off key imports, including medicines.

And more sanctions are likely. Congress has begun preparing legislation, with wide bipartisan support, that could seek to impose a near total trade embargo on Iran.

Yet with international diplomacy with Iran stalled, some administration officials may be ready to offer sweeteners to give Iran a face-saving way to resume negotiations.

At the last round of talks, in February in Kazakhstan, the United States and five other world powers offered Tehran modest concessions, including softening limits on trade using gold and other precious metals, and easing some restrictions on petrochemical exports, if the Iranians agreed to halt production of medium-enriched uranium. The Iranians did not accept the offer.

"I think some people in the administration may be inclined to throw the Iranians a bone with more concessions" in the months ahead, said Michael Singh, a former Bush White House aide. He added that he doesn't believe the strategy will work.

American officials are concerned that Iran is intent on developing nuclear weapons; leaders in Tehran contend they are developing nuclear capabilities for strictly civilian purposes.

Many in official Washington consider the Iran Project's views the wishful thinking of liberals who give Iran's hard-line leaders more credit than they deserve. The State Department appeared to play down differences with the group, saying in a statement that it shares a desire to use "rigorous sanctions and serious negotiations" to draw Iran into talks.

"We will give diplomacy every chance to succeed," said a senior administration official. "But ultimately, the onus is on Iran," said the official, who declined to be identified, citing the sensitivity of the subject.

If the administration did offer concessions, it would risk a clash with Congress and with Israel, which don't want to ease pressure until Tehran commits to irrevocable curbs on its nuclear program.

As he began the markup this month on a new sanctions bill that already had 340 cosponsors, Rep. Ed Royce (R-Fullerton), chairman of the House Foreign Affairs Committee, was unyielding. "We attack Iran's oil exports, crimp its access to overseas cash, and hit its brutal leaders," he said. The committee later passed the bill unanimously.

Crocker, who is 63 and retired last year, believes the hard-line approach won't pay off.

His voice carries weight in foreign policy circles. Crocker served in Tehran early in his diplomatic career. He served as U.S. ambassador to Iraq, Syria, Lebanon, Kuwait and Pakistan, and was dean of the Bush School of Government and Public Service at Texas A&M University.

In his view, history shows that Tehran won't yield to anything less than the all-out war it faced from Iraq in the 1980s. But Iranian authorities, he argues, may be open to compromise if they see it in their interest.

In a report last month, the Iran Project asserted that sanctions may have intensified government repression and corruption, and spurred Iran to accelerate its nuclear program.

"Each increment of pressure may have begotten a new increment of defiant expansion," the report said.